Current monitor

ABSTRACT

A current monitor is provided for indicating the presence of the short duration current pulses necessary to detonate ordnance devices and simultaneously interrupt the ordnance firing circuit to simulate firing conditions. The current monitor consists of a reed switch magnetically linked to the firing circuit by a low resistance coil in series with the firing circuit. The normally opened reed switch is connected in series with the monitor power source and the control gate of a silicon controlled rectifier. The monitor source of power is also connected in series with a relay and the anode of the silicon controlled rectifier, the relay being adapted, upon activation, to both interrupt the firing circuit and to generate an instrumentation signal indicative of the presence of the required current flow in the firing circuit. In operation a current pulse sufficient to detonate the ordnance device will cause the reed switch to close and trigger the silicon controlled rectifier. When the silicon rectifier is triggered, the current will be permitted to flow through the relay thereby interrupting the firing circuit and producing the instrumentation signal. Since the current is no longer flowing through the firing circuit, the reed switch will open, but this will not interrupt the flow of current through the relay since the silicon controlled rectifier will continue to conduct once it has been triggered. Thus, the relay remains activated and the instrumentation signal is maintained until the circuit is reset.

United States Patent [72] Inventor John E. Williams San Jose, Calif. [2 l Appl. No. 731,588 [22] Filed May 23, 1968 [45] Patented Apr. 6, l 971 [73] Assignee United Aircraft Corporation East Hartford, Conn.

[54] CURRENT MONITOR Primary Examiner-Donald .l. Yusko Assistant Examiner-Daniel Myer AtlorneySteven F. Stone ABSTRACT: A current monitor is provided for indicating the presence of the short duration current pulses necessary to detonate ordnance devices and simultaneously interrupt the ordnance firing circuit to simulate firing conditions. The current monitor consists of a reed switch magnetically linked to the firing circuit by a low resistance coil in series with the firing circuit. The normally opened reed switch is connected in series with the monitor power source and the control gate of a silicon controlled rectifier. The monitor source of power is also connected in series with a relay and the anode of the silicon controlled rectifier, the relay being adapted, upon activation, to both interrupt the firing circuit and to generate an instrumentation signal indicative of the presence of the required current flow in the firing circuit. In operation a current pulse sufficient to detonate the ordnance device will cause the reed switch to close and trigger the silicon controlled rectifier. When the silicon rectifier is triggered, the current will be permitted to flow through the relay thereby interrupting the firing circuit and producing the instrumentation signal. Since the current is no longer flowing through the firing circuit, the reed switch will open, but this will not interrupt the flow of current through the relay since the silicon controlled rectifier will continue to conduct once it has been triggered. Thus, the relay remains activated and the instrumentation signal is maintained until the circuit is reset.

\J LATCHING T SWITCH J HN E. wai 4,95%.

+ 28V DC LATCHING SWITCH CH'FLRE AY PATENT'EDAPR 61971 ATTORNEY FIG. 2

CURRENT MONITOR BACKGROUND OF THE INVENTION This invention relates to current monitors and more particularly to current monitors capable of responding to short duration current pulses such as are obtained in the firing circuits of ordnance devices.

In complex ordnance'systems such as, for example, those encountered in the ignition and separation systems employed in rocket motors, the failure mode is generally through some defect in the firing circuit rather than in a defect in the detonation circuit within the ordnance device itself. This is particularly true since most electrically initiated squibs are provided with redundant circuitry to ensure detonation of the device if an adequate signal is applied thereacross. Thus, in the testing of such systems, it is'common to substitute a dummy explosive device in the firing circuit, which dummy device has an electrical resistance identical with that of the live device. In checking the integrity of such a firing circuit, the detection means must be capable of picking up extremely short duration current pulses and relatively complex detection systems are required. The existing ordnance circuit verification units are quite complex and do not provide isolation between the firing circuit and the detection circuit thereby introducing characteristic variations between the test and actual firing conditions. In addition, such devices are difficult to calibrate and the reproducibility of the outputs is often suspect.

According to this -invention, however, a simple current monitor is provided which provides isolation between the firing circuit and the monitoring circuit and in addition has the capability of simulating an actual firing by breaking the firing circuit in response to a current sufficient to detonate a live device. The currentmonitor of this invention is also capable of detecting current flow in either direction which is particularly important in complex aerospace type applications where, for example, stray currents generated in the firing circuit as a result of the operation of the associated electronic guidance equipment must be detected. Further, the capability of simulating the actual firing will permit the test to show the effect of the stray currents generated by the firing pulse upon the other electronic equipment in a device.

It is accordingly an object of this invention to provide a current monitor capable of detecting short duration current pulses.

It is another object of this invention to provide a current monitor capable of detecting short duration current pulses flowing in either direction in a circuit.

It is another object of this invention to provide a current monitor which will interrupt a circuit in response to flow ofa predetermined current pulse therethrough.

It is another object of this invention to provide a current monitor whose circuitry is electrically isolated from that of the circuit to be monitored.

It is another object of this invention to provide a current monitor having a negligible effect on the character of the circuit to be monitored.

These and other objects of this invention will be readily apparent from the following description with reference to the accompanying drawings wherein:

FIG. 1 is a schematic circuit diagram of one embodiment of this invention, and

FIG. 2 is a schematic circuit diagram of another embodiment of this invention.

DESCRIPTION OF THE INVENTION are calibrated in ampere turns and have a response time in the microsecond ranges. The number of turns in coil 4 will be selected to close reed switch 3 when a current level equal to that required to detonate the live ordnance device corresponding to dummy device 2 is flowing in the firing circuit. Thus, if a 4 ampere current would be required to detonate the live ordnance device and a 20 ampere-turn reed switch is employed, the coil would have 5 turns. Reed switch 3 is connected in series to the power source and to the trigger of a latching switch shown generally as 5. Relay 6 is also connected in series with the 28 volt power source and latching switch 5. The latching switch 5 functions to prevent flow of current through relay 6 until reed switch 3 is closed. When reed switch is closed, current flows to the latching switch trigger which then permits current to flow through relay 6 and will continue to permit the current to flow through relay 6 even through reed switch 3 is subsequently opened as will be explained hereinafter. Various types of latching switches can be employed and may consist of a latching relay or a thyratron type circuit or a Silicon Controlled Rectifier (SCR), for example, with the SCR being preferred. Thus, as illustrated the relay 6 is connected to the anode 7 of the SCR and reed switch 3 is connected through current limiting resistance 8 to the trigger or gate 10 of the SCR. It is also preferable to employ a desensitizing resistor 9 asis known in the art. Reset switch 12 is connected to the cathode ll of the silicon controlled rectifier. Relay 6 operates to interrupt the firing circuit by opening switch 14 and to complete the instrumentation circuit 15 by closing switch 13. In operation the current monitor will be connected in series with the firing circuit and dummy load as shown. When a current of the required intensity flows through the firing circuit, reed switch 3 will close. This will permit the current to flow through the reed switch into the trigger of the SCR, triggering the same and permitting the current to flow through relay 6 which is mechanically linked to normally opened switch 15 and normally closed switch 14. Relay 6 will then open switch 14 in the firing circuit and will close switch 15 in the instrumentation circuit. When switch 14 is opened reed switch 3 will open since current is no longer flowing in the coil 4. However, current will continue to flow through relay 6 since the latching switch 5 will remain in the conducting condition permitting current flow therethrough even though the triggering signal is no longer present. The monitor can be replaced in its original condition by opening and closing reset switch 12 which then resets the latching circuit. As can be seen the current monitor operates not only to produce a steady instrumentation signal as a result of a short duration pulse of current but also simulates the actual firing of the ordnance device by breaking the firing circuit. This feature will produce a complete simulation of the conditions occurring in an actual firing such as the generation of any stray currents which are produced as a result of the interruption of the firing circuit by the detonation of the explosive device. In addition, the current monitor is capable of monitoring currents in the firing circuits flowing in any direction. Thus, if during the test some of the associated electronic equipment caused stray currents to flow through the firing circuit, which currents would have sufficient intensity to detonate the ordinance device 2, these currents will be monitored and an instrumentation signal indicative of detonation will be generated.

In a particular system in which a 4-ampere current was required to detonate the explosive device, coil 4 was composed of five turns of number 14 wire and 20-ampere turn reed switch was employed. A 2N2323 SCR was used and the values of resistances 8 and 9 were 3.8 kilohms and ohms respectively. A 390 ohm, 100 milliampere, 28 volt relay coil was employed. Such a monitor has a tested capability of detecting current pulses as short as 50 microseconds.

Referring now to FIG. 2, another embodiment of the invention is shown which embodiment has the capability of producing an instrumentation signal indicative of firing in response to either a current pulse of the required intensity as in the embodiment of FIG. I or a current pulseof lesser intensity but which exists for a period of time adequate to cause a hazard to the explosive device. Thus, for example, where an explosive device is designed to be detonated by a short duration pulse of 5 amperes, such a device could be endangered by a current flow 3 amperes which exists for 58 milliseconds, for example.

Referring now to FIG. 2, an embodiment of the invention is shown which has the capability of detecting either an instantaneous pulse of magnitudes sufficient to set off the explosive device or a continuous current flow of a lesser magnitude for a predetermined period of time which would be adequate to endanger the explosive device. In FIG. 2 like reference numerals refer to the same elements as shown in FIG. 1. Thus, the lefthand portion of the circuit comprising the relay 6, latching switch 5, reed switch 3, coil 4 and relay actuated switches 13 and 14 are the same as described with respect to FIG. 1.

To provide for the additional capability of detecting the lower current for a specific period of time, another reed switch 3' is magnetically linked to the firing circuit by means of low resistance coil 4. Since the current to be detected is of a lesser magnitude than is to be detected by reed switch 3, a greater number of turns is required in coil 4'. Thus, if reed switch 3 is a ampere turn switch and the current to be detected is 3 amperes, coil 4' would have 6.66 turns. Reed switch 3 is connected electrically to the trigger of latching switch 5 and to the power source with a time delay circuit 20 interposed between the trigger of latching switch 5 and reed switch 3. Latching switch 5' may be identical to latching switch 5.

The time delay circuit 20 consists of resistor 21 and capacitor 22 which are selected to produce a time constant equal to the desired delay. A reference diode is used to produce a constant and predetermined voltage that will develop the predetermined time delay upon the closing of reed switch 3'. Thus, for example, ifa time delay of 58 milliseconds is desired, resistor 21 would be 33,000 ohms and capacitor 22 would be 20 microfarads and the reference diode 23 will produce an 18 volt output. The operation of this device is basically similar to that of FIG. 1. When a current of4 amperes flows through the firing circuit 2, reed switch 3 will close and permit the current and voltage from the 28 volt power source to be applied to the trigger of latching switch 5. When triggered, latching switch 5 will permit current to flow through relay 6 which will open switch 14 and break the firing circuit and close switch 13 to provide the instrumentation signal output. When switch 14 is opened, reed switch 3 will open but switch 5 will remain conductive until the reset button 12 is pressed as described above. If, however, the current flowing through the firing circuit is below 4 amperes and not sufficient to trigger reed switch 3 but is at least 3 amperes, reed switch 3 will close. This will permit the current to flow through the reed switch to the time delay circuit. If the current flows for a period of time equal to the time delay then latching switch 5 will be triggered. However, if the lower current pulse is of a lesser duration, reed switch 3' will open before a signal is sent to the trigger of latching switch 5 and no further operation of the device will occur. However, if the current pulse lasts for the required duration of time which for the purpose of this example is assumed to be 58 milliseconds then latching switch 5' will be triggered and permit current to flow through relay 6, thereby opening switch 14 and closing switch 13 in the manner previously described.

As described above, when the firing circuit is broken by the opening of switch 14 the latching switch 5 will remain conductive until reset by means of switch 12.

While this invention has been described with respect to various embodiments thereof, it is readily apparent that other modifications of the invention could be made. For example, a multichannel current monitor could be utilized in which more than one firing circuit is monitored by the use of separate reed switches for each channel to be monitored. Accordingly, these embodiments should be considered as illustrative rather than limiting of the invention. The invention itself being limited only by the following claims.

lclaim:

1. A current monitor capable of detecting the flow of current of a predetermined level in a circuit to be monitored and capable of interrupting the circuit to be monitored upon the detection of a flow of current of said predetermined level therein, said current monitor comprising:

a. a source of DC power distinct from the source of power in said circuit to be monitored;

b. a latching switch comprising a normally nonconductive element and a trigger element adapted to render said nonconducting element conductive upon application of an electrical signal to said trigger element;

c. a normally open reed switch in series with said source of DC power and the trigger means of said latching switch;

(:1. a relay connected in series with said source of said DC power and the normally nonconductive element of said latching switch;

e. means for generating an instrumentation signal in response to the flow of current through said relay;

f. coil means for producing a magnetic field adequate to activate said reed switch upon the flow of current of said predetermined level through said coil a normally closed switch connected in series with said coil means said switch being operatively connected to said relay whereby said switch will open upon activation of said relay; and

h. means for connecting said coil means and said normally closed switch means in series with said circuit to be monitored;

whereby flow of a predetermined current level through said circuit to be monitored will cause said reed switch to close thereby permitting an electrical signal from said DC power source to be applied to said latching switch rendering said latching switch conductive and permitting the flow of current from said source of DC power through said relay to cause a generation of the instrumentation signal and the interruption of the circuit to be monitored.

2. The current monitor of claim 1 further comprising time delay circuit means operatively connected between said reed switch and the trigger of said latching switch, said time delay circuit means delaying the triggering of the latching switch until said current to be monitored has existed in said circuit for a predetermined period of time whereby the activation of said relay means is delayed.

3. The current monitor of claim 1 further comprising means for detecting the flow of a current in said circuit to be monitored at a second lower predetermined level for a predetermined period of time said means comprising:

a. a second latching switch comprising a normally nonconductive element and a trigger element adapted to render said nonconducting element conductive upon application of an electrical signal to said element;

b. a second normally opened reed switch in series with said source of DC power;

c. second coil means for producing a magnetic field adequate to activate said second reed switch upon the flow of a current of said second predetermined level through said second coil means;

d. time delay circuit means operatively connected between said second reed switch and the trigger of said second latching switch, said time delay means delaying the activation of said trigger means of said second latching switch until said current has existed in said circuit to be monitored at said second lower predetermined level for said predetermined period of time; and

e. current carrying means connecting the normally nonconductive element of said second latching switch to said relay;

whereby flow of current at said first predetermined level will generate an instrumentation signal and cause interruption of said circuit to be monitored by means of said first latching switch and whereby flow of current in said circuit to be monitored at a level equal to or greater than said second lower predetermined level but less than said first predetermined level will cause a generation of an in- 5. The current monitor of claim 2 wherein said latching strumentation signal and interruption of said circuit to be switch comprises a silicon controlled rectifier.

monitored by means of said second latching switch only if The Current monitor of Claim 3 wherein S firs! and said current exists for said predetermined period of time. Second latching Switches Comprises Silicon Controlled 4. The current monitor of claim 1 wherein said latching 5 rectifier?- switch comprises a silicon controlled rectifier. 

1. A current monitor capable of detecting the flow of current of a predetermined level in a circuit to be monitored and capable of interrupting the circuit to be monitored upon the detection of a flow of current of said predetermined level therein, said current monitor comprising: a. a source of DC power distinct from the source of power in said circuit to be monitored; b. a latching switch comprising a normally nonconductive element and a trigger element adapted to render said nonconducting element conductive upon application of an electrical signal to said trigger element; c. a normally open reed switch in series with said source of DC power and the trigger means of said latching switch; d. a relay connected in series with said source of said DC power and the normally nonconductive element of said latching switch; e. means for generating an instrumentation signal in response to the flow of current through said relay; f. coil means for producing a magnetic field adequate to activate said reed switch upon the flow of current of said predetermined level through said coil g. a normally closed switch connected in series with said coil means said switch being operatively connected to said relay whereby said switch will open upon activation of said relay; and h. means for connecting said coil means and said normally closed switch means in series with said circuit to be monitored; whereby flow of a predetermined current level through said circuit to be monitored will cause said reed switch to close thereby permitting an electrical signal from said DC power source to be applied to said latching switch rendering said latching switch conductive and permitting the flow of current from said source of DC power through said relay to cause a generation of the instrumentation signal and the interruption of the circuit to be monitored.
 2. The current monitor of claim 1 further comprising time delay circuit means operatively connected between said reed switch and the trigger of said latching switch, said time delay circuit means delaying the triggering of the latching switch until said current to be monitored has existed in said circuit for a predetermined period of time whereby the activation of said relay means is delayed.
 3. The current monitor of claim 1 further comprising means for detecting the flow of a current in said circuit to be monitored at a second lower predetermined level for a predetermined period of time said means comprising: a. a second latching switch comprising a normally nonconductive element and a trigger element adapted to render said nonconducting element conductive upon application of an electrical signal to said element; b. a second normally opened reed switch in series with said source of DC power; c. second coil means for producing a magnetic field adequate to activate said second reed switch upon the flow of a current of said second predetermined level through said second coil means; d. time delay circuit means operatively connected between said second reed switch and the trigger of said second latching switch, said time delay means delaying the activation of said trigger means of said second latching switch until said current has existed in said circuit to be monitored at said second lower predetermined level for said predetermined period of time; and e. current carrying means connecting the normally nonconductive element of said second latching switch to said relay; whereby flow of current at said first predetermined level will generate an instrumentation signal and cause interruption of said circuit to be monitored by means of said first latching switch and whereby flow of current in said circuit to be monitored at a level equal to or greater than said second lower predetermined level but less than said first predetermined level will cause a generation of an instrumentation signal and interruption of said circuit to be monitored by means of said second latching switch only if said current exists for said predetermined period of time.
 4. The current monitor of claim 1 wherein said latching switch comprises a silicon controlled rectifier.
 5. The current monitor of claim 2 wherein said latching switch comprises a silicon controlled rectifier.
 6. The current monitor of claim 3 wherein said first and second latching switches comprises silicon controlled rectifiers. 